Continuous Femoral Nerve block: After aseptic skin disinfection and sterile draping of the inguinal region, a 38 mm broadband 13-6 MHz linear array ultrasound (US) probe (Philips HD 11XE, Bothell, WA) will be placed on the skin to locate the position of the femoral nerve at the inguinal crease. The ultrasound transducer will be covered with a sterile, transparent dressing TegadermTM HP (3M Heath Care, St. Paul, MN). Sterile conductivity gel Ultra/Phonic (Pharmaceutical Innovations TM, Newark, NJ) will be used. In plane or out of plane approach will be used to guide the tuohy needle towards the femoral nerve. A skin wheal will be raised with 2 to 3 mLs of local anesthetic solution (1% lidocaine), peripheral nerve stimulator (PNS) with an initial current output of 1mA (frequency 2Hz, pulse width 0.1ms) will be used to verify the type of evoked muscle response. The stimulating tuohy needle will be inserted at 45º angle to the skin, 1 cm lateral to the femoral artery pulsation towards the femoral nerve under ultrasound guidance. The anesthesiologist will seek either sartorius or quadriceps muscle evoked muscle response based on the random number allocation in sealed opaque envelopes. The stimulating needle will be adjusted and once the appropriate muscle twitch was obtained at a current of less than 0.4 mA, the catheter will be threaded 3-5 cm pass the needle tip while maintaining spread of local anesthetic solution in a short axis view. Plain ropivacaine 0.5% mixed with lidocaine 1% will be injected in increments of 5 mL after negative aspiration up to a total of 20 mL. To determine the spread of local anesthetic agent we divided the area around the femoral nerve into 8 pie-chart sectors with the femoral nerve in the middle. For documentation we will use a piece of transparency film with the pie chart of eight even sectors drawn on it . The film will be positioned over the US image such that the center of the pie chart is positioned on the middle of the femoral nerve and the upper edge of the film is parallel to the upper edge of the US image. Having done this, we could determine the local anesthetic spread and compare it between the two groups. Time to femoral nerve location (time needle entered the skin to localization of plexus with adequate twitch), time to catheter insertion (start to end of catheter insertion) and time to completion of drug injection (start to end of drug injection) will be documented.